Hydrotreating catalyst composition and processes therefor and therewith

ABSTRACT

A catalyst composition and a process for hydrodealkylating a C 9  + aromatic compound to a C 6  to C 8  aromatic hydrocarbon such as a xylene are disclosed. The composition comprises an alumina and hexavalent chromium oxide. The process comprises contacting a fluid which comprises a C 9  + aromatic compound with the catalyst composition under a condition sufficient to effect the conversion of a C 9  + aromatic compound to a C 6  to C 8  aromatic hydrocarbon. Also disclosed is a process for producing the composition which comprises: (1) contacting an alumina, which can be optionally calcined before being contacted, with a hexavalent chromium-containing compound in a liquid medium under a condition sufficient to incorporate the hexavalent chromium-containing compound into the alumina to form a chromium-modified alumina wherein the volume of the liquid medium is larger than the bulk volume of alumina; (2) removing the excess liquid medium containing the hexavalent chromium compound; (3) drying the chromium-modified alumina; and (4) calcining the chromium-modified alumina to a chromium-promoted alumina under a condition sufficient to effect the conversion of the hexavalent chromium compound to corresponding chromium oxide.

FIELD OF THE INVENTION

This invention relates to a catalyst composition useful for converting aC₉ + aromatic compound to a C₆ to C₈ aromatic hydrocarbon, a process forproducing the composition, and a process for using the composition in ahydrodealkylation process.

BACKGROUND OF THE INVENTION

It is well known to those skilled in the art that aromatic hydrocarbonsare a class of very important industrial chemicals which find a varietyof uses in petrochemical industry. Recent efforts to convert gasoline tomore valuable petrochemical products have therefore focused on thearomatization of gasoline to aromatic hydrocarbons by catalytic crackingin the presence of a catalyst. The aromatic hydrocarbons produced by thearomatization process include C₆ to C₈ hydrocarbons such as benzene,toluene and xylenes (hereinafter collectively referred to as BTX) whichcan be useful feedstocks for producing various organic compounds andpolymers. However, heavier, less useful aromatic compounds are alsoproduced during the aromatization process. It is, therefore, highlydesirable to convert these compounds to the more useful BTX.

Though a metal oxide-promoted alumina such as Cr/Al₂ O₃ has been used ascatalyst in a hydrodealkylation process, the conversion of a C₉ +aromatic compound and the selectivity to BTX are generally not as highas one skilled in the art would desire. One possibility for the lowselectivity is that the metal oxide is not uniformly dispersed on thealumina support thereby limiting the total surface area of the catalyst.Therefore, there is an ever-increasing need to develop an improvedcatalyst and a process for converting these heavier and less usefularomatic compounds to the more valuable BTX hydrocarbons (hereinafterreferred to as hydrodealkylation process). Such development would alsobe a significant contribution to the art and to the economy.

SUMMARY OF THE INVENTION

An object of this invention is to provide a catalyst composition whichcan be used to convert a C₉ + aromatic compound to a C₆ to C₈ aromatichydrocarbon. Also an object of this invention is to provide a processfor producing the catalyst composition. Another object of this inventionis to provide a process which can employ the catalyst composition toconvert C₉ + aromatic compounds to C₆ to C₈ aromatic compounds. Anadvantage of the catalyst composition is that it exhibits highhydrodealkylation activity, satisfactory yield of xylenes and BTX, andgood stability. Other objects and advantages will becomes more apparentas this invention is more fully disclosed hereinbelow.

According to a first embodiment of the present invention, a compositionwhich can be used as a catalyst for converting a C₉ + aromatic compoundto a C₆ to C₈ aromatic hydrocarbon is provided. The composition is achromium-promoted alumina.

According to a second embodiment of the invention, a process forproducing a composition which can be used as catalyst in ahydrodealkylation process is provided. The process comprises, consistsessentially of, or consists of: (1) contacting an alumina, which can beoptionally calcined before being contacted, with a hexavalentchromium-containing compound in a liquid medium under a conditionsufficient to incorporate the hexavalent chromium-containing compoundinto the alumina to form a chromium-modified alumina wherein the volumeof the liquid medium is larger than the bulk volume of alumina; (2)removing the excess liquid medium containing the hexavalent chromiumcompound; (3) drying the chromium-modified alumina; and (4) calciningthe chromium-modified alumina to a chromium-promoted alumina under acondition sufficient to effect the conversion of the hexavalent chromiumcompound to corresponding chromium oxide.

According to a third embodiment of the present invention, a processwhich can be used for converting a C₉ + aromatic compound to a C₆ to C₈aromatic compound is provided which comprises, consists essentially of,or consists of, contacting a fluid which comprises a C₉ + aromaticcompound, optionally in the presence of an inert fluid such as ahydrogen-containing fluid, with a catalyst composition which can beprepared by the process disclosed above in the second embodiment of theinvention under a condition effective to convert a C₉ + aromaticcompound to an aromatic hydrocarbon containing 6 to 8 carbon atoms permolecule.

DETAILED DESCRIPTION OF THE INVENTION

According to the first embodiment of the invention, a composition whichcan be used as catalyst in a hydrodealkylation process for converting aC₉ + aromatic compound to a C₆ to C₈ aromatic hydrocarbon is provided.The composition can comprise, consist essentially of, or consist of, ahexavalent chromium-promoted alumina wherein the hexavalent chromium ispresent in the composition in a BTX selectivity-improving amount toimprove the selectivity to BTX when the composition is used in ahydrodealkylation process.

According to the first embodiment of the invention, the weight ratio ofelemental chromium to the alumina can be any ratio so long as the ratiocan improve the BTX selectivity during a hydrodealkylation process forconverting of a C₉ + aromatic compound to a C₆ to C₈ aromatichydrocarbon. Generally, the ratio can be in the range of from about0.0001:1 to about 1: 1, preferably about 0.0005:1 to about 1:1, morepreferably about 0.001:1 to about 0.8:1 and most preferably from 0.005:1to 0.5:1 for an effective dehydroalkylation conversion. Alternatively,chromium can be present in the catalyst composition in the range of fromabout 0.001 to about 50, preferably about 0.005 to about 50, morepreferably about 0.1 to about 45, and most preferably 0.01 to 33 gramsper 100 grams of the catalyst composition.

The alumina can be α-alumina, β-alumina, γ-alumina, η-alumina,δ-alumina, or combinations of any two or more thereof. The presentlypreferred alumina is a γ-alumina having a surface area in the range offrom about 40 to about 300 m² /g, a total pore volume in the range offrom about 0.1 to about 1 ml/g.

Any methods known to one skilled in the art for incorporating achromium-containing compound or a portion thereof into an alumina suchas, for example, impregnation or extrusion can be employed for producingthe composition of the present invention. However, it is presentlypreferred the composition be produced by the process disclosed in thesecond embodiment of the invention.

According to the second embodiment of the present invention, the aluminacan be α-alumina, β-alumina, γ-alumina, η-alumina, δ-alumina, orcombinations of any two or more thereof. The presently preferred aluminais γ-alumina having a surface area in the range of from about 40 toabout 300 m² /g, a total pore volume in the range of from about 0.1 toabout 1 ml/g. These aluminas are commercially available.

An alumina is generally first treated with an aqueous solution of ahexavalent chromium-containing compound. An alumina can be optionallycalcined before it is used in the second embodiment of the invention toremove any possible contaminant(s) in the alumina. The condition forcalcining an alumina can be any condition known to one skilled in theart. The calcining can also be carried out under the condition disclosedhereinbelow.

According to the present invention, any hexavalent chromium-containingcompound which, when incorporated into an alumina, can effect theimprovement of selectivity to BTX or xylene or both in ahydrodealkylation process can be employed. Presently it is preferredthat a trivalent chromium compound be excluded. Examples of suchcompounds include, but are not limited to, ammonium chromate, ammoniumdichromate, alkali metal chromates, alkali metal dichromates, alkalineearth metal chromate, alkaline earth metal dichromate, chromiumtrioxides, chromic acid, chromium hexacarbonyl, and combinations of anytwo or more thereof. The presently preferred hexavalent chromiumcompound is an ammonium or alkali metal chromate for it is inexpensiveand readily available.

Generally, in the first step of the process of the second embodiment ofthe invention, an alumina can be combined with a hexavalentchromium-containing compound in any suitable weight ratios which wouldresult in the formation of a chromium-promoted alumina disclosed in thefirst embodiment of the invention. Such combination is carried out in asuitable liquid medium, preferably an aqueous medium, to form anequilibrium alumina-chromium mixture.

Generally, if chromium is a cation of the chromium-containing compoundwhen in aqueous solution, the aqueous solution is acidic. On the otherhand, if the chromium is in the anion portion of the chromium-containingcompound such as Na₂ CrO₄, the aqueous solution is in the alkaline pH.Any compounds known to prepare an acidic or alkaline aqueous solutioncan be employed in the present invention. It is presently preferred thatthe hexavalent chromium compound is present in the mixture in excess tothe quantity that can be filly absorbed by an alumina. Therefore, thevolume of the aqueous solution containing the hexavalent chromiumcompound is greater than the total or bulk volume of the alumina.Furthermore, the weight ratio of the chromium compound to alumina can bein the range of from about 0.001:1 to about 100:1, preferably about0.01:1 to about 10:1, and most preferably 0.1:1 to 5:1. The combining ofan alumina and a hexavalent chromium-containing compound can be carriedout at any temperature. Generally, the temperature can be in the rangeof from about 25° to about 250° C., preferably about 40° to about 250°C., and most preferably 50° to 150° C. under any pressure, preferablyatmospheric pressure, for any length so long as the hexavalent chromiumcompound and the alumina are well mixed, generally about 1 minute toabout 250 hours, preferably about 1 hour to about 150 hours. Generally,the aqueous medium, as disclosed above, can be either acidic, oralkaline. It is presently acidic because an ammonium or alkali metalchromate is the presently preferred hexavalent chromium-containingcompound.

Upon completion of incorporating the chromium-containing compound intoan alumina, a chromium-modified alumina is formed. In the next step ofthe process, the excess solution containing the chromium-containingcompound is removed. It is presently preferred that thechromium-modified alumina is not washed. The removal of the excesssolution can be carried out by any methods known to one skilled in theart. Examples of suitable removal methods include filtration,decantation, centrifugation, or combinations of any two or more thereof.

Thereafter, the chromium-modified alumina can be dried under anyconditions known to one skilled in the art such as, for example, airdrying at any temperature. Air drying can be carried out at atemperature for about 25° to about 150° C. for about 1 minute to about30 hours under any pressure such as atmospheric pressure. There is nowashing of the chromium-modified alumina before drying.

In the next step, the chromium-modified alumina is subject tocalcination under a condition that can include a temperature in therange of from about 300° to about 1000° C., preferably about 350° toabout 750° C., and most preferably 400° to 650° C. under a pressure inthe range of from about 1 to about 10, preferably about 1 atmospheresfor a period in the range of from about 1 to about 30, preferably about1 to about 20, and most preferably 1 to 15 hours. Upon calcination, achromium (oxide)-promoted alumina is formed.

The chromium-modified alumina can also be treated with a steam under asuitable condition sufficient to effect the conversion of thechromium-containing compound, which have been incorporated into thealumina, to its corresponding oxide form. The chromium-modified aluminacan be air dried as disclosed above to remove most moisture contentbefore being steam-treated. The air-dried chromium-modified alumina canthen be treated with a steam. Generally the steam temperature can be inthe range of from about 120° to about 1500° C., preferably about 200° toabout 1200° C., and most preferably 250° to 1000° C. The treatmentperiod can be as short as 5 minutes to as long as about 30 hours so longas it is sufficient to convert the chromium compound to its oxide form.The treatment can be carried out under a pressure in the range of fromabout atmospheric pressure to about 2,000, preferably to about 1,500,and most preferably to 1000 psig. The chromium-promoted alumina, i.e.,the calcined product disclosed above, can also be steam-treated toimprove catalytic activity, or catalyst selectivity, or both.

The composition of the invention thus prepared then can be, if desired,pretreated with a reducing agent before being used in ahydrodealkylation process. The presently preferred reducing agent is ahydrogen-containing fluid which comprises molecular hydrogen (H₂) in therange of from 1 to about 100, preferably about 5 to about 100, and mostpreferably 10 to 100 volume %. The reduction can be carried out at atemperature, in the range of from about 250° to about 800° C. for about0.1 to about 10 hours preferably about 300° to about 700° C. for about0.5 to about 7 hours, and most preferably 350° to 650° C. for 1 to 5hours.

According to the third embodiment of the present invention, a processuseful for converting a C₉ + aromatic compound to a C₆ to C₈ aromatichydrocarbon comprises, consists essentially of, or consists ofcontacting a fluid stream comprising a C₉ + aromatic compound and,optionally, in the presence of an inert fluid such as, for example,hydrogen-containing fluid, with a catalyst composition under a conditionsufficient to effect the conversion of a C₉ + aromatic compound to a C₆to C₈ aromatic hydrocarbon. The inert fluid can be hydrogen, nitrogen,helium, argon, carbon dioxide, neon, steam, and combinations of any twoor more thereof. The presently preferred inert fluid is ahydrogen-containing fluid. The inert fluid can also be fed separatelyinto contact with a C₉ + aromatic compound and a catalyst. The catalystcomposition can be the same as that disclosed in the first embodiment ofthe invention.

The term "fluid" is used herein to denote gas, liquid, vapor, orcombinations of two or more thereof. The term "C₉ + aromatic compound"is referred to, unless otherwise indicated, as a substituted aromaticcompound containing at least 9 carbon atoms per molecule. Preferably thesubstituted aromatic compound has the formula of R_(q) Ar wherein each Ris a hydrocarbyl radical having 1 to about 15 carbon atoms and isindependently selected from the group consisting of alkyl radicals, arylradicals, alkaryl radicals, aralkyl radicals, alkenyl radicals, andcombinations of any two or more thereof, q is a whole number from 1 to5, and Ar is an aryl, preferably a phenyl, group. More preferably R isan alkyl radical having 1 to about 10 carbon atoms and the aromaticcompound has 9 to about 16 carbon atoms per molecule. Most preferablythe aromatic compound contains 9 to 12 carbon atoms per molecule.

Any fluid which contains a C₉ + aromatic compound as disclosed above canbe used as the feed for the process of this invention. The origin ofthis fluid feed is not critical. However, a preferred fluid feed is aC₉ + aromatic compound derived from the heavies fraction of a productfrom a paraffin, in particular gasoline, aromatization reaction.Generally, this heavies fraction contains primarily trimethylbenzenessuch as 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, and1,3,5-trimethylbenzene and tetramethylbenzenes such as1,2,3,4-tetramethylbenzene, 1,2,3,5-tetramethylbenzene and1,2,4,5-tetramethylbenzene. Additionally, n-propylbenzene,3-ethyltoluene, 4-ethyltoluene, 3-n-propyltoluene, 4-n-propyltoluene,and 1,3-diethylbenzene can also be present in the fluid. Benzene,toluene, ethylbenzene and xylenes are generally substantially absentfrom the fluid, i.e., the amount of each of these aromatic hydrocarbonsis less than about 0.1 weight %. Thus, there is no significantalkylation of these lower aromatic hydrocarbons by the C₉ + aromaticcompound, i.e., no significant transalkylation occurs as a side-reactionin the process of this invention.

Any hydrogen-containing fluid which comprises, consists essentially of,or consists of, molecular hydrogen (H₂) can be used in the process ofthis invention. This hydrogen-containing fluid can therefore contain H₂in the range of from about 1 to about 100, preferably about 5 to about100, and most preferably 10 to 100 volume %. If the H₂ content in thefluid is less than 100%, the remainder of the fluid may be any inert gassuch as, for example, N₂, He, Ne, Ar, steam, or combinations of any twoor more thereof, or any other fluid which does not significantly affectthe process or the catalyst composition used therein.

The contacting of a fluid containing a C₉ + aromatic compound, in thepresence or absence of a hydrogen-containing fluid, with a catalystcomposition can be carried out in any technically suitable manner, inbatch, semicontinuous, or continuous process under a condition effectiveto convert a C₉ + aromatic compound to a C₆ to C₈ aromatic hydrocarbon.Generally, a fluid containing a C₉ + aromatic compound, preferably beingin the vaporized state, and a hydrogen-containing fluid are introducedinto a fixed catalyst bed, or a moving catalyst bed, or a fluidizedcatalyst bed, or combinations of any two or more thereof by any meansknown to one skilled in the art such as, for example, pressure, meterpump, and other similar means. The condition can include an hourly spacevelocity (HSV) of the C₉ + aromatic compound fluid stream in the rangeof about 0.01 to about 100, preferably about 0.05 to about 50, and mostpreferably 0.1 to 30 g feed/g catalyst/hour. The hydrogen-containingfluid hourly space velocity generally is in the range of about 1 toabout 10,000, preferably about 5 to about 7,000, and most preferably 10to 5,000 ft³ H₂ /ft³ catalyst/hour. The preferred molar ratio of H₂ tothe C₉ + aromatic compound can be in the range of from about 0.01:1 toabout 20:1, preferably about 0.1:1 to about 10:1, and most preferably0.5:1 to 5:1. Generally, the pressure can be in the range of from about30 to about 1000 psig, preferably about 50 to about 750 psig, and mostpreferably 200 to 600 psig, and the temperature is about 250° to about1,000° C., preferably about 350° to about 800° C., and most preferably400° to 650° C.

The process effluent generally contains a heavies fraction ofunconverted C₉ + aromatics and other heavy (C₉ +) aromatic compoundswhich may have been formed by side-reactions (such as isomerization); alights fraction of alkanes, mainly methane, ethane, propane, n-butane,isobutane, and minor amounts (about 0.1 to about 5 weight %) of C₅ andC₆ alkanes such as, for example, isopentane and n-pentane; and a BTXaromatic hydrocarbons fraction (benzene, toluene, ortho-xylene,meta-xylene and para-xylene). Generally, the effluent can be separatedinto these principal fractions by fractionation distillation which iswell known to one skilled in the art. The heavies fraction can berecycled to a hydrodealkylation reactor described above, the lightsfraction can be used as fuel gas or as a feed for other reactions suchas, for example, in a thermal cracking process to produce ethylene andpropylene, and the BTX fraction can be further separated into individualC₆ to C₈ aromatic hydrocarbon fractions. Alternatively, the BTX fractioncan undergo one or more reactions either before or after separation toindividual C₆ to C₈ hydrocarbons so as to increase the content of themost desired BTX aromatic hydrocarbon. Suitable examples of suchsubsequent C₆ to C₈ aromatic hydrocarbon conversions aredisproportionation of toluene (to form benzene and xylenes) involvingtransalkylation benzene and xylenes (to form toluene), and isomerizationof meta-xylene and/or ortho-xylene to para-xylene.

After the catalyst composition has been deactivated by, for example,coke deposition or feed poisons, to an extent that the feed conversionand/or the selectivity to the most valuable C₆ to C₈ aromatic product(generally xylenes) have become unsatisfactory, the catalyst compositioncan be reactivated by any means known to one skilled in the art such as,for example, calcining in air to burn off deposited coke and othercarbonaceous materials, such as oligomers or polymers, preferably at atemperature of about 400° to about 650° C., followed by a treatment witha reducing agent such as, for example, with hydrogen gas at atemperature of about 400° to about 600° C. The optimal time periods ofthe calcining and treatment with a reducing agent depend generally onthe types and amounts of deactivating deposits on the catalystcomposition and on the calcination and reduction temperatures. Theseoptimal time periods can easily be determined by those possessingordinary skills in the art and are omitted herein for the interest ofbrevity.

The following examples are presented to further illustrate thisinvention and are not to be construed as unduly limiting the scope ofthe present invention. The examples illustrate the preparation ofcatalyst compositions of the invention and the use of the composition ina hydrodealkylation process.

A γ-alumina obtained as 1/16 inch extrudates from Criterion CatalystCompany L.P. (Michigan City, Ind.) was used. First, 100 g of the aluminawas calcined in air at 525° C. for 3 hours to remove any contaminants. Aportion of the alumina (14 g) was well mixed at 25° C. with 28.08 g of20 weight % (NH₄)₂ CrO₄ (ammonium chromate) and 2.80 g of 70 weight %HNO₃ solution. The resulting mixture in a thick wall tube was sealed andheated at 80° C. for 88 hours to form a chromium-modified alumina.Thereafter, the excess solution containing ammonium chromate was removedby filtration. After drying in air at room temperature (25° C.) forabout 8 hours, the dried, chromium-modified alumina was calcined at 538°C. for 6 hours in a maffle furnace (air) to produce 15.34 a calcinedchromium oxide-promoted alumina or Cr⁺⁶ /Al₂ O₃ containing 7.60 weight %of chromium oxide (Invention Catalyst A). The chromium oxide content wasdetermined by X-ray fluorescence spectrometry (XRF) employing a SiemensMRS 400 multi-channel spectrometer.

Secondly, 14 g of the calcined γ-alumina was well mixed with 8.58 g of amixture containing 20 weight % ammonium chromate solution underincipient wetness (impregnation condition) to impregnate all ammoniumchromate onto the alumina, dried as above, and followed by calcining at538° C. for 6 hours in air to produce 15.20 g of chromium oxide-promotedalumina (Control Catalyst B) containing 7.43 weight % of chromium oxideby calculation.

Thirdly, 14.0 g of the calcined γ-alumina was well mixed with a solutioncontaining 12 g of Cr(NO₃)₃.9H₂ O, 4.0 g of NH₄ OH, and 20 g H₂ O in ajar at 25 ° C. followed by the same procedure described above forpreparing Invention Catalyst A to produce 13.07 g of a chromium(III)oxide-incorporated alumina containing 6.30 weight % chromium(III) oxide(Control Catalyst C). The chromium oxide content was determined by XRFspectrometry described above.

These catalysts were then employed, according to the third embodiment ofthe invention, in a hydrodealkylation process for converting a C₉ +aromatic compound to BTX. The liquid feed in the hydrodealkylation runswas heavy C₉ + aromatic compounds obtained in a gasoline aromatizationprocess in which gasoline was converted into BTX and C₉ + aromaticcompounds. The composition of the feed is given in Table I whichcontained less than 2 ppm S. Not given in Table I are numerouscomponents which were in very small quantities and, in some instances,whose chemical structures were unknown.

                  TABLE I                                                         ______________________________________                                        Composition of Feed                                                           Feed Component        Weight Percent                                          ______________________________________                                        c-Hexene-2            1.104                                                   1-Methyl-3-ethylbenzene                                                                             2.254                                                   1-Methyl-4-ethylbenzene                                                                             1.057                                                   1,3,5-Trimethylbenzene                                                                              1.958                                                   1-Methyl-2-ethylbenzene                                                                             1.306                                                   1,2,4-Trimethylbenzene                                                                              9.977                                                   1,2,3-Trimethylbenzene                                                                              3.060                                                   1-Methyl-3-I-propylbenzene                                                                          0.286                                                   2,3-Dihydroindene     2.845                                                   1,3-Diethylbenzene    1.173                                                   1-Methyl-3-n-propylbenzene                                                                          1.543                                                   1,4-Diethylbenzeneylbenzene                                                                         0.910                                                   1-Methyl-4-n-propylbenzene                                                                          0.328                                                   n-Butylbenzene-ethylbenzene                                                                         2.836                                                   1-Methyl-2-n-propylbenzene                                                                          0.889                                                   1,4,-Dimethyl-2-ethylbenzene                                                                        1.991                                                   s-C5-benzene/1,3-dimethyl-4-ethylbenzene                                                            2.958                                                   1,2-Dimethyl-4-ethylbenzene                                                                         3.454                                                   1,2-Dimethyl-3-ethylbenzene                                                                         1.007                                                   1,2,4,5-Tetramethylbenzene                                                                          1.936                                                   1,2,3,5-Tetramethylbenzene                                                                          2.695                                                   5-Methylindan         3.004                                                   1-Ethyl-2-n-propylbenzene                                                                           1.592                                                   2-Methylindan         3.040                                                   1,3-Di-I-propylbenzene                                                                              1.084                                                   Naphthalene           4.767                                                   2-Methylnaphthalene   3.382                                                   1-Methylnaphthalene   1.184                                                   ______________________________________                                    

A stainless-steel reactor tube (inner diameter 0.75 inch; length 20inches) was filled with a 20 ml bottom layer of Alundum® alumina (inert,low surface area alumina), one of the catalysts (in 1/16 inchextrudates) in the center position 5 ml, and a 20 ml top layer ofAlundum® alumina. The catalysts were pretreated with hydrogen (260ml/minute) at 575° C. (starting at 25° C. then ramping at 10° C./min)for one hour. The feed was then introduced into the reactor at a rate of20 milliliters/hour, together with hydrogen gas at a rate of 260 ml ofH₂ /hours. The reaction temperature was 573° to 579° C. as shown inTable II, and the reaction pressure was 500 psig. The reactor effluentwas cooled and analyzed with an on-line gas chromatograph at intervalsof about 1 hour. The results are shown in Table II.

                                      TABLE II                                    __________________________________________________________________________               Catalyst                                                                          Reaction                                                                             Reactor Effluent (wt %).sup.a                                 Incorp.                                                                            Weight                                                                            Temp                                                                             Time         Conversion                                     Catalyst                                                                            Method.sup.b                                                                       (g) (°C.)                                                                     (hr)                                                                              BTX                                                                              Xyl                                                                              C.sub.9.spsb.+                                                                   %.sup.c                                        __________________________________________________________________________    Invention A                                                                         EDF  3.24                                                                              575                                                                              5.87                                                                              33.5                                                                             19.6                                                                             52.4                                                                             47.6                                           Control B                                                                           IMP  3.47                                                                              576                                                                              5.48                                                                              16.2                                                                             11.5                                                                             73.2                                                                             26.8                                           Control C                                                                           EDF  3.02                                                                              578                                                                              5.77                                                                              11.5                                                                             8.5                                                                              76.2                                                                             23.8                                           __________________________________________________________________________     .sup.a The values presented, except conversion, are weight percent. Xyl       denotes the total weight % of all xylenes.                                    .sup.b Incorporation method: IMP, incipient wetness impregnation with         impregnating solution; EDF, invention process,                                equilibriumdeposition-filtration method.                                      .sup.c The % conversion was calculated as 100%  weight % C.sub.9.spsb.+. 

The results shown in Table II indicate that the invention catalyst A,which was promoted with Cr⁺⁶ and made by the invention process, hadsignificantly higher yield of BTX and xylenes than control catalysts B(promoted with Cr⁺⁶ and made by conventional impregnation) and controlcatalyst C (promoted with Cr⁺³ and made by EDF method as described inTable II).

The results clearly demonstrate that the present invention is welladapted to carry out the objects and attain the ends and advantagesmentioned as well as those inherent therein. While modifications may bemade by those skilled in the art, such modifications are encompassedwithin the spirit of the present invention as defined by the disclosureand the claims.

That which is claimed:
 1. A process comprising contacting a C₉ +aromatic compound-containing fluid with a catalyst composition under acondition sufficient to effect the conversion of a C₉ + aromaticcompound to a C₆ to C₈ aromatic hydrocarbon wherein said catalystcomposition is prepared by the steps which comprise: (1) contacting analumina with a hexavalent chromium-containing compound in a liquidmedium under a condition sufficient to incorporate said hexavalentchromium-containing compound into said alumina to form achromium-modified alumina wherein the volume of said liquid medium islarger than the bulk volume of alumina; (2) removing the excess liquidmedium containing the hexavalent chromium-containing compound; (3)drying said chromium-modified alumina; and (4) calcining saidchromium-modified alumina under a condition sufficient to effect theconversion of said hexavalent chromium-containing compound tocorresponding chromium oxide.
 2. A process according to claim 1 whereinsaid C₉ + aromatic compound has the formula of R_(q) Ar wherein each Ris a hydrocarbyl radical having 1 to about 15 carbon atoms and isindependently selected from the group consisting of alkyl radicals, arylradicals, alkaryl radicals, aralkyl radicals, alkenyl radicals, andcombinations of any two or more thereof, q is a whole number from 1 to5, and Ar is an aryl group.
 3. A process according to claim 1 whereinsaid C₉ + aromatic compound comprises an aromatic hydrocarbon selectedfrom the group consisting of 1,2,3-trimethylbenzene,1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene,1,2,3,4-tetramethylbenzene, 5 1,2,3,5-tetramethylbenzene,1,2,4,5-tetramethylbenzene, n-propylbenzene, 3-ethyltoluene,4-ethyltoluene, 3-n-propyltoluene, 4-n-propyltoluene,1,3-diethylbenzene, and combinations of any two or more thereof.
 4. Aprocess according to claim 1 wherein said C₉ + aromatic compound isderived from a heavies fraction of a product from a paraffinaromatization process.
 5. A process according to claim 4 wherein saidparaffin is gasoline.
 6. A process according to claim 1 wherein saidcontacting of said C₉ + aromatic compound-containing fluid with saidcomposition is carried out in the presence of a hydrogen-containingfluid.
 7. A process according to claim 6 wherein said process is carriedout under a condition which comprises a liquid hourly space velocity ofsaid fluid in the range of about 0.1 to about 30 g feed/g catalyst/hour,a gas hourly space velocity of said hydrogen-containing fluid in therange of about 10 ft³ gas/ft³ catalyst/hour to about 5,000 ft³ /ft³catalyst/hour, a molar ratio of hydrogen to said C₉ + aromatic compoundin the range of about 0.5:1 to about 5:1, a pressure in the range ofabout 50 psig to about 750 psig, and a temperature in the range of about250° to about 1000° C.
 8. A process according to claim 7 wherein saidcondition comprises a pressure of about 200 to about 600 psig and atemperature of about 400° to about 650° C.
 9. A process according toclaim 8 wherein said C₉ + aromatic compound comprises an aromatichydrocarbon selected from the group consisting of1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene,1,2,3,4-tetramethylbenzene, 1,2,3,5-tetramethylbenzene,1,2,4,5-tetramethylbenzene, n-propylbenzene, 3-ethyltoluene,4-ethyltoluene, 3-n-propyltoluene, 4-n-propyltoluene,1,3-diethylbenzene, and combinations of any two or more thereof.
 10. Aprocess according to claim 1 wherein said liquid medium is an acidicaqueous solution.
 11. A process according to claim 1 wherein saidhexavalent chromium-containing compound is selected from the groupconsisting of ammonium chromate, ammonium dichromate, alkali metalchromates, alkali metal dichromates, alkaline earth metal chromate,alkaline earth metal dichromate, chromium trioxides, chromic acid,chromium hexacarbonyl, and combinations of any two or more thereof. 12.A process according to claim 1 wherein said hexavalentchromium-containing compound is ammonium chromate.
 13. A processaccording to claim 1 wherein said condition in step (1) furthercomprises a period in the range of from about 1 to about 150 hours. 14.A hydrodealkylation process comprising contacting, in the presence of ahydrogen-containing fluid, a fluid comprising C₉ + aromatic compoundwith a catalyst composition under a condition sufficient to effect theconversion of said C₉ + aromatic compound to a C₆ to C₈ aromatichydrocarbon wherein said catalyst composition is prepared by the stepscomprising: (1) contacting an alumina, which is calcined before beingcontacted, with a hexavalent chromium-containing compound in an aqueoussolution under a condition sufficient to incorporate said hexavalentchromium-containing compound into the alumina to form achromium-modified alumina wherein the volume of said aqueous solution islarger than the bulk volume of said alumina; (2) removing the excessaqueous solution containing said hexavalent chromium-containingcompound; (3) drying said chromium-modified alumina; and (4) calciningsaid chromium-modified alumina under a condition sufficient to effectthe conversion of said hexavalent chromium-containing compound tocorresponding chromium oxide wherein:said C₉ + aromatic compound has theformula of R_(q) Ar wherein each R is a hydrocarbyl radical having 1 toabout 15 carbon atoms and is independently selected from the groupconsisting of alkyl radicals, aryl radicals, alkaryl radicals, aralkylradicals, alkenyl radicals, and combinations of any two or more thereof,q is a whole number from 1 to 5, and Ar is an aryl group; said processis carried out under a condition which comprises a liquid hourly spacevelocity of said fluid in the range of about 0.1 to about 30 g feed/gcatalyst/hour, a gas hourly space velocity of said hydrogen-containingfluid in the range of about 10 ft³ gas/ft³ catalyst/hour to about 5,000ft³ /ft³ catalyst/hour, a molar ratio of hydrogen to said C₉ + aromaticcompound in the range of about 0.5:1 to about 5:1, a pressure in therange of about 50 psig to about 750 psig, and a temperature in the rangeof about 250° to about 1000° C.; said aqueous solution is an acidicsolution; and said hexavalent chromium-containing compound is selectedfrom the group consisting of ammonium chromate, ammonium dichromate,alkali metal chromates, alkali metal dichromates, alkaline earth metalchromate, alkaline earth metal dichromate, chromium trioxides, chromicacid, chromium hexacarbonyl, and combinations of any two or morethereof.
 15. A process according to claim 14 wherein said C₉ + aromaticcompound comprises an aromatic hydrocarbon selected from the groupconsisting of 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene,1,3,5-trimethylbenzene, 1,2,3,4-tetramethylbenzene,1,2,3,5-tetramethylbenzene, 1,2,4,5-tetramethylbenzene, n-propylbenzene,3-ethyltoluene, 4-ethyltoluene, 3-n-propyltoluene, 4-n-propyltoluene,1,3-diethylbenzene, and combinations of any two or more thereof; saidcondition comprises a pressure of about 200 to about 600 psig and atemperature of about 400° to about 650° C.; and said hexavalentchromium-containing compound is ammonium chromate.
 16. A processaccording to claim 15 wherein said C₉ + aromatic compound is derivedfrom a heavies fraction of a product from a paraffin aromatizationprocess.
 17. A process according to claim 16 wherein said paraffin isgasoline.
 18. A process according to claim 14 wherein said hexavalentchromium-containing compound is ammonium chromate.
 19. Ahydrodealkylation process comprising contacting a C₉ + aromaticcompound, in the presence of hydrogen, with a catalyst which is producedby the steps comprising: (1) incorporating a calcined alumina withammonium chromate solution to produce a Cr-incorporated alumina whereinthe volume of said ammonium chromate solution is larger than the bulkvolume of said alumina; (2) removing excess ammonium chromate solutionfrom said Cr-incorporated alumina; (3) drying said Cr-incorporatedalumina; and thereafter (4) calcining said Cr-incorporated alumina.